A slipper clutch is usually combined with the spur gear. The purpose of a slipper clutch is to, just as the name implies, slip. The way a slipper clutch works is two pads clamp down onto the spur gear with a spring to provide the tension. The looser the slipper clutch is, the less traction and speed you will have. The tighter the slipper clutch is, the easier it will be to pull wheelies, possibly burn out if the conditions are correct, while also significantly increasing the chances of stripping the gears.